INVERSION

Inversion involves putting an auxiliary verb before the subject of a clause. We do this in a number of different situations:

Questions

The most common use of inversion is in the forming of questions. We use the auxiliary verbs be (for progressive and passive forms), have (for perfect forms) and do (for most other forms). Modal verbs can also be inverted to form questions:
Were they ready when you arrived?
Where was it made?
Have you ever visited France?
Where do you live?
What should we do now?

Negative and restrictive adverbs

In formal English, it is quite common to use inversion after negative adverbial expressions and restrictive words such as only, never, hardly and little.
At no time did he get permission for what he was doing.
Not until the next morning did she realise how serious it was.
Only later did they learn his terrible secret.
Never before have I seen such awful behaviour.
Hardly had we walked in the door when the phone started ringing.
Little do you know how much trouble you are in.

So, nor and neither

Inversion is common when using these words to expression agreement or disagreement.
I'm from Turkey. So am I.
I don't like monsters! Nor/Neither do I.
Conditional clauses
In formal English, the if clause in conditional sentences can be rephrased through inversion:
Were you to win the election, what's the first thing you'd do? = If you won the election …
Had we known what the weather would be like, we wouldn't have come = If we had known what …

May

When we are making wishes, we can use inversion:
May you both live happily ever after!

Exclamations

We can use inversion to make exclamations:
Aren't you a silly girl!
Isn't it a lovely day!

ANOTHER WAY OF EXPLAINING IT...

En inglés la inversión es obligatoria en preguntas directas:
auxiliar + sujeto + verbo
Are you coming tomorrow?(¿Vienes mañana?)
Does she start early?(¿Empieza temprano?)
Can the boy be here?(¿El chico puede estar aquí?)


Con may para expresar deseos
May you have good luck!(¡Que tengas suerte!)
May they be happy!(¡Que sean felices!)


Con "tampoco" (neither) , "ni" (nor) y "también" (so) respectivamente:
neither / nor / so + auxiliar afirmativo + sujeto
She's angry and I am too.She's angry and so am I.(Está enfadada y yo también.)
They won't tell you and Bob won't either. They won't tell you and neither will Bob.(No te lo dirán y Bob tampoco.)
Beth can't come and her sister can't either. Beth can't come nor can her sister.(Beth puede venir ni su hermana también.)

• La inversión también se utiliza para dar énfasis o ser retórico en situaciones formales, discursos, en las noticias y en literatura sobre todo.
• En oraciones encabezadas por adverbios o locuciones adverbiales de lugar seguidos por "be" o un verbo de movimiento:
HERE / THERE / IN / UP... + be, come , go... + sujeto
Here's Bob, he is early.(Aquí está Bob, llega pronto.)
There comes your friend.(Alli viene tu amigo.)On the doorstep was the homeless sleeping!(¡En la puerta de casa estaba durmiendo el sin-techo!)
Down fell three of them.(Abajo cayeron tres de ellos.)
Cuando el sujeto es PRONOMBRE, NO hay inversión:
Up they are.(Están arriba.)
Back he went again.(Volvió de nuevo.)
• Detrás de expresiones adverbiales negativas o restrictivas :
locución adverbial + auxiliar AFIRMATIVO + sujeto + verbo
at no time
en ningún momento
by no means
de ninguna manera
in / under no circumstances
bajo ningún concepto
neither ... nor
ni ... ni
nowhere
en ningún sitio
not till / not until
hasta que no
on no account
de ningún modo
They can't accept this situation under any circunstances.Under no circumstances can they accept this situation.(Bajo ningún concepto pueden aceptar esta situación.)
We can't be held responsible in any way.In no way can we be held responsible.(De ningún modo podemos ser considerados responsables.)
Bob hadn't seen anywhere a larger house. Nowhere had Bob seen a larger house.(En ningún sitio había visto Bob una casa mayor.)
He didn't realize that he had lost his keys until / till he got home.Not till / Not until he got home did he realize that he had lost his keys.(No fue hasta llegar a casa cuando se dio cuenta de que había perdido las llaves.)

A la hora de "re-escribir" la oración ("rephrasing") observa que la oración principal está en forma negativa pero el "rephrasing" tiene que llevar el verbo afirmativo al ser ya el adverbio negativo:
You can't use my computer at any time. At no time can you use my computer. (En ningún momento puedes utilizar mi ordenador.)


En comparaciones detrás de:
little
poco, poca
never
nunca
rarely
raramente, raras veces
seldom
rara vez
so
tan
such
tal

She little knew that he was a compulsive gambler.Little did she know that he was a compulsive gambler.(Poco sabía ella que era un jugador compulsivo.)
I have never been offered such a presentNever have I been offered such a present.(Nunca me han ofrecido un regalo así.)
He rarely buys a round.Rarely does he buy a round.(Raras veces paga una ronda.)
We had seldom seen him looking so happy.Seldom had we seen him looking so happy.(Rara vez lo habíamos visto tan feliz.)
The soap opera is so exciting that I forget all my aches.So exciting is the soap opera that I forget all my aches.(Tan emocionante está la telenovela que olvido todos mis achaques.)
The popularity of the film will be so great that everybody will want to see it.Such will the popularity of the film be that everybody will want to see it.(Tal será la popularidad del la película que todo el mundo querrá verla.)


Oraciones correlativas(cuando una acción ocurre inmediatamente detrás de otra)
hardly ... when
apenas ... cuando
scarcely ... when
apenas ... cuando
no sooner ... than
No hacer nada más que ... cuando
He hardly falls asleep when his neighbour begins playing loud music. Hardly does he fall asleep when his neighbour begins playing loud music.(Apenas se duerme cuando su vecino empieza a poner la música alta.)
They had scarcely got into bed when the doorbell rang.Scarcely had they got into bed when the doorbell rang.(Apenas se habían metido en la cama cuando el timbre de la puerta sonó.)
I will no sooner arrive, they will all start to argue.No sooner will I arrive than they all will start to argue.(No habré hecho nada más que llegar cuando empezarán todos a discutir.)


Detrás de expresiones adverbiales que empiecen por "only
He could make himself see only by jumping. Only by jumping could he make himself see.(Sólo saltando pudo hacerse ver.)
I remembered his name only after he left.Only after he left did I remember his name.(Sólo cuando se marchó me acordé de su nombre.)
She will know what happened only then.Only then will she know what happened.(Sólo entonces sabrá lo que ocurrió.)


En las oraciones condicionales con were, should o had es posible la inversión omitiendo if:
If I were in his shoes, I wouldn't do that. Were I in his shoes, I wouldn't do that. .(De estar en su lugar, no haría eso.)
If you should see her, give her this envelope.Should you see her, give her this envelope.(Si la vieras, dale este sobre.)
If they had come earlier, they would have seen him.Had they come earlir, they would have seen him.(Si hubieran venido antes, lo habrían visto.)